L0301P93 - Parasitic Infections
Parasites *an organism which lives upon or within another living organism at whose expense it obtains some advantage Parasitic Diseases *commonly refers to diseases caused by **helminths (metazoans) ***multicellular eukaryotic organisms (worms) with complex life cycle **protozoans ***unicellular eukaryotic organisms **ectoparasites ***arthropods attached to human hosts ****mosquito, ticks, leeches - do not cause disease themselves but transmit them *typical of developing countries Helminths *3 main groups **nematodes (round worms) **platyhelminths (flat worms) ***cestodes (tapeworms) ***trematodes (flukes) *adults may be centimetres or metres long *usually extracellular habitat *generally live in body cavities **e.g. intestines and blood stream *but can attack virtually all organs *over a million species, most: nematodes *most common in tropical/subtropical regions Life Cycle *direct —> reproductive stages are released and directly infect a host **e.g. active skin penetration  or faecal-oral transmission ***ingestion of eggs/larvae originating from faeces of an infected host *indirect —> reproductive stages must first go through an intermediate host or vector **e.g. via meats and insect bites Filariasis Cause *Brugia malayi or Wuchereria bancrofti Distribution *tropical disease *endemic in around 80 countries worldwide **particularly subsaharan Africa, PNG Transmission *by blood-feeding vectors, e.g. mosquito, fly *reside in lymph node until adulthood —> travel to the skin to be picked up by vectors Symptoms *lymphatic system **cause dilation and dysfunction *subcutaneous tissue **larvae causes intense irritation Example: Brugi Malayi *causes elephantiasis **limb becomes grossly enlarged due to obstruction of the lymphatic vessels *often results in secondary infections of these areas as they are hard to clean *tissue damage usually remains even after elimination the parasite *cannot be caused by just one worm, normally result from multiple mosquito bites Diagnosis *blood smears and/or PCR tests Treatment *ivermectin, albendazole, diethylcarbamazine *hygiene to prevent secondary infections Prevention *mosquito control *no vaccine available Protozoa *single-celled eukaryotes (2-100 μm) *mostly free living in the environment but some are human parasites Transmission *insect **malaria, trypanosome, leishmania *ingestion of infective stages **cryptosporidium, toxoplasma *venereal transmission (STDs) **trichomonas Kinetoplastids *flagellated parasites with kinetoplasts *two main groups: **trypanosomes **leishmania Trypanosomes American Trypanosomiasis (Chagas Disease) Cause *Trypanosoma cruzi Distribution *16-18 million infected, kills 50,000/year *mainly in Central and South America Transmission *indirect - by the Triatomine bug **pass T. cruzi parasites in their faeces **often bite on the face around the eyes **ingests T.cruzi in “blood meals” **infection occurs when faeces are rubbed into a wound, eyes or mouth *direct **eating uncooked foods **congenital - from mother to child **person-to-person by blood transfusions Symptoms *2 phases of disease *acute: **fever, fatigue, headache, loss of appetite, diarrhoea and vomiting **swelling of glands, swelling at sign of parasite entry (often the eyelids) *chronic: **infection may remain silent for decades **slowly destroys the parasympathetic nervous system, i.e. may lead to ***cardiac complications —> enlarged heart = arrhythmias —> heart failure ***intestinal complications —> enlarged oesophagus and colon—> eating and defecating problems Diagnosis *presence of parasite in blood smears, serology, muscle biopsies Treatment *very difficult to cure infection *anti-parasitics - nifurtimox, benznidazole Prevention *avoid poor quality dwellings *bed net, insect repellent, protective clothing *avoid contaminated food and water sources *no vaccine available African Trypanosomiasis (Sleeping Sickness) Cause *Trypanosome brucei Distribution *sub-saharan Africa *25,000-45,000 new cases each year Transmission *indirect - by the Tsetse fly **inject T. brucei parasite when taking a blood meal **T. brucei develops in body fluids and returns to fly when it takes blood meal Symptoms *development or red sore at site of bite *fever, severe headache, extreme fatigue, aching muscles/joints, swollen lymph glands *CNS destruction: progressive confusion, ataxia, personality, slurred speech, seizures *death can result after ever weeks to months after infection if left untreated Diagnosis *presence of parasites in blood samples, lumbar puncture (cerebrospinal fluid), skin and lymph node biopsies, serology Treatment *should commence as soon as possible **few effective drugs in advanced disease *requires hospitalisation *drugs **acute stage ***Suramin, Pentamidine (some resistance), Eflornithine¹ (newer drug) **chronic stage with CNS involvement ***Arsenical drugs - Melarsoprol ¹an essential drug but too expensive for common use Prevention *protective clothing - thick, green materials,(fly attracted to dark and bright colours) *insect repellent *avoid moving vehicles (fly attached to dust) *pentamidine for prophylaxis *no vaccine available T.Brucei Antigenic Variation *undergo repeated antigenic variation of surface glycoproteins *can evade antibody mediated lysis and form the next wave of infection Leishmaniasis Cause *Leishmania species **particularly L. major, L. tropics, L. infant, L. donovani, L. mexicana Distribution *geographically diverse **occurs in tropical and subtropical regions on all continents, except Australia *2 million new cases each year *1/10 world’s population is at risk of infection Transmission *indirect - by the sandfly via bite *many natural hosts include rodents, small mammals and dogs Symptoms *several different forms *visceral **invasion of macrophages in liver, spleen **causes gross swelling of the abdomen *cutaneous **most common but least serious **invasion of skin tissues *mucosal **invasion of mucosal tissues Diagnosis *travel history *sores that wont heal *organ and/or skin biopsy for microscopic examination *blood tests (antibody response) Treatment *antimonial drugs **can cause birth defects and not taken during early stages of pregnancy *Pentamidine **drugs vary depending on species and geographic location *parasite resistance is a problem Prevention *insect repellent, clothing, bed nets *stay indoors or well screened areas from dusk to dawn *no vaccine available Giardiasis Cause *Giardia lamblia - flagellated round parasite Distribution *worldwide - one of the most common water-borne diseases Symptoms *appear one to two weeks after infection and generally resolves themselves *diarrhoea leading to weight loss/dehydration *stomach aches *malabsorption of fats —> greasy stools *nausea Transmission *once infected, parasite lives in the intestines and is passed in faeces in its cyst form *contamination of food and water sources leads to direct faecal-oral transmission Diagnosis *stool samples analysis Treatment *drink fluids to prevent dehydration *albendazole, metronidazole or tinidazole Prevention *good hygiene practices *avoid contaminated food and water sources *currently no vaccine available Apicomplexa *presence of specialised organelles **Rhoptry, Micronemes, Apicoplast **allow them to invade cells more easily *range of veterinary and human diseases **toxoplasmosis **malaria Toxoplasmosis Cause *Toxoplasma gondii *highly successful parasite - lives in many different organisms Distribution *worldwide *estimated between 30-65% of the population infected with T. gondii, but few are symptomatic **~90% of the population in France due to common raw meat dishes Transmission *T. gondii reproduce in cats and form cysts which are excreted in faeces *ingestion of cat faeces (cat litter, gardening) *ingestion of undercooked meat *contaminated drinking water Symptoms *normal people **flu-like, swollen lymph glands, muscle aches and pains **symptoms resolve over time  *pregnant and immunocompromised people **serious health problems **pregnant women (foetus) ***foetal abnormalities (eye and brain damage, jaundice) and death **immunocompromised individuals ***i.e. AIDS and transplant patients Diagnosis *serology Treatment *healthy individuals **symptoms abate within weeks to months **leads to chronic infection *pregnant/immunocompromised individuals **range of medications ***pyrimethamine ***sulfadiazine ***spiramycin *no vaccine available Malaria Cause *Plasmodium species **most dangerous - P. falciparum Distribution *more than1/3 of the world’s population lives within malaria endemic areas **tropical regions: subsaharan Africa, south America, Papua New Guinea, Indonesia *~1-2million people die from malaria each year, mostly children under the age of 5 Transmission *indirect: by mosquito **female mosquito bites person/animal and injects saliva which contains the parasite **parasite travels to the liver and into the blood stream where it affects RBCs *person to person **potential source of transmission when a person becomes immune to malaria, but still has parasites in their blood stream Symptoms *flu-like symptoms - chills, fever, sweats *P. falciparum: **creates sticky knobs on RBC —> adhere to the vascular endothelium **prevents parasite from passing through the spleen where the immune system normally operates **can build up —> occlude blood flow and cause tissue damage, particularly severe if it occurs in the brain Diagnosis *presentation of symptoms *blood smears Treatment *range of drugs as resistance is high **Quinine, Chloroquine, Artemisinin **Artemisinin Combination Therapies (ACT) *new experimental vaccine available **given to infants and young children **only approximately 30% efficacy Prevention *insect repellent *bed nets *mosquito only comes out after dark *Malarone prophylaxis **Atovaquone/Proguanil *Doxycycline prophylaxis **expensive and has many side effects